(a) Field of the Invention
The present invention relates to a polymer type copper conductive composition for use in an electronic circuit, and more particularly to a copper conductive composition having both a satisfactory conductivity and an excellent solderability by employing spherical copper powder coated with silver as its metal powder and employing resol type phenolic resin containing a dimethylene ether bond in bonded formaldehyde by 5% or more as a binder.
(b) Description of the Prior Art
In general, a polymer type copper conductive composition for use in an electronic circuit or the like needs to have an excellent solderability for the purpose of readily conducting the soldering of wire lead or the like. A known copper conductive composition of the type having solderability is disclosed in Japanese Patent Laid-Open No. 64-34597. The composition as disclosed above consists of resol type phenolic resin, a saturated fatty acid, an unsaturated fatty acid, or their metal salt, a metal powder, a metal chelate forming agent, and a soldering agent. According to this invention, the metal chelate forming agent is added for the purpose of preventing the oxidation of the metal copper powder and an excellent solderability is obtained by adding the soldering agent.
However, it is necessary to add an antioxidant for the purpose of preventing the metal powder from oxidation and to add the soldering agent. Therefore, although an excellent solderability can be obtained, the conductivity is insufficient. On the contrary, another conventional type in which a satisfactory conductivity is realized suffers from its poor solderability. A composition that can exhibit both an excellent solderability with respect to cured films and satisfactory conductivity has not been as yet obtained. Therefore, it is necessary to individually use a composition exhibiting a satisfactory conductivity and another composition which exhibits an excellent solderability, or it is necessary to apply metal plating to a circuit on which a copper paste has been previously printed and cured.
The methods described above encounter a problem in that the manufacturing process is complex. In particular, the latter method suffers from another problem in terms of the disposal of waste liquid which raises the cost.